The quality of crude oil throughout the world is reduced by acidic components found in the oil. During refining, at temperatures between 220 and 400° C., these species can become corrosive. Acidic species such as naphthenic acids that have boiling points in this temperature range will condense on metal surfaces leading to damage in the refinery infrastructure, potential safety issues, and costly repairs. As a result, oils with high acid content, whether from conventional (crude oil) or oil sands (bitumen) sources, are more difficult to market and their value is significantly discounted.
Conventional methods to remove corrosive species from crude oil involve costly and energy-intensive chemical and thermal processes. For example, the current technologies developed to remove organic acids from crude oil involve either thermal decomposition at 400° C. (Blum et al. in U.S. Pat. No. 5,820,750), adsorbing onto inert materials (Varadaraj in U.S. Pat. No. 6,454,936), treating with surfactants (Gorbaty et al. in Canadian Patent 2,226,750) or converting the organic acids into various derivatives that are easier to remove (Brons in U.S. Pat. No. 5,871,637, Sartori et al. in Canadian Patents 2,343,769 and 2,345,271, and Varadaraj et al. in U.S. Pat. No. 6,096,196).
Efforts to minimize organic acid corrosion have included a number of approaches for neutralizing and removing the acids from the oil. For example, there are numerous approaches in the literature on the reduction of the organic acid species in crude oil. They include thermal decomposition of organic acids using high temperatures in the presence (U.S. Pat. Nos. 5,914,030, 5,928,502) or absence (U.S. Pat. No. 5,820,750) of a metal catalyst and treatment of corrosive acids with group IA and IIA metal oxides, hydroxides and hydrates to form metal salts of naphthenic acids which are then thermally decomposed at elevated temperatures (U.S. Pat. Nos. 5,985,137, 5,891,325, 5,871,637, 6,022,494, 6,190,541, 6,679,987). Other methods include chemical formation of esters of the organic acids in the presence of alcohol and a base (U.S. Pat. Nos. 5,948,238, 6,251,305, 6,767,452, and Canadian Patent 2,343,769), reducing acidity by the formation of various salts of organic acids using base (U.S. Pat. Nos. 5,643,439, 5,683,626, 5,961,821, 6,030,523), removal of naphthenic acids using detergents or surfactants (U.S. Pat. Nos. 6,054,042, 6,454,936), absorbing organic acids onto polymeric amines (U.S. Pat. Nos. 6,121,411, 6,281,328) and by adding corrosion inhibitors to crude oil to prevent naphthenic acid induced metal corrosion (U.S. Pat. No. 5,552,085).
U.S. Pat. No. 6,258,258 and Canadian Patent 2,345,271 describe the formation of naphthenic acid amides by treating crude oil with excess ammonia at elevated temperatures (above 180° C.) and elevated pressures (100-400 kPa).
While these processes have achieved varying degrees of success, most of these methods are costly and energy-intensive and their effectiveness somewhat limited. As a result, there is a need to develop alternative approaches to eliminate the corrosive species in petroleum and for treating acidic crudes.
Recently it has been reported that lipase B (Mickiyo in European Patent 0287634), from the fungi Candida Antarctica, produced by industrial enzyme producer Novozymes, demonstrated catalytic activity in the hydrolysis of fatty acids and converts them into fatty acid esters in the presence of alcohol (Anderson et al. in Biocat. Biotrans. 1998, 16, 181-204). The enzyme also has the ability to convert fatty acids, carboxylic acids and triglycerides into amides by the addition of amines or ammonia (DeZoete et al. in PCT Patent Application PCT/EP1994/003038 with publication number WO 95/07359; DeZoete et al. in Ann. NY Acad. Sci. 1996, 799, 346-350; Egraz in U.S. Pat. No. 5,973,203; Hacking et al. in Biotech. Bioeng. 2002, 68, 84-91; Ignacio et al. in Chem. Soc. Rev. 2004, 33, 201-9; Irimescu et al. in Tet. Lett. 2004, 45, 523-525; Litjens et al. in PCT WO 00/58490; Madeira Lau et al. in Org. Lett. 2000, 2, 4189-4191; and Tuccio et al. in Tet. Lett. 1991, 32, 2763-2764).
However, the art is substantially bereft of methods for upgrading the quality of crude oil comprising naphthenic acids by the use of enzymes or biocatalysts. U.S. Pat. Nos. 7,101,410, 6,461,859 and 5,358,870 describe the use of biocatalysts, such as bacteria, fungi, yeast, and algae, hemoprotein, and a cell-free enzyme preparation from Rhodococcus sp. ATCC 53969, respectively, to improve the quality of oil specifically target organic sulphur containing molecule by reducing the sulphur content as well as lowering their viscosity. U.S. Pat. No. 5,858,766 describes the use of microorganisms (a bacteria strain) in a bioupgrading capacity to selectively remove organic nitrogen and sulphur in oil as well as remove metals.
There remains the need for bioprocesses, as an attractive alternative to current upgrading methods, that use enzymes to improve the quality of crude oil and bitumen by removing acidic species.